A desiccant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its vicinity. Commonly known pre-packaged desiccants are solids that adsorb water. These desiccants can, for example, comprise silica, activated charcoal, calcium sulfate, calcium chloride, and molecular sieves (typically zeolites).
In many desiccants combinations of several moisture adsorbing materials are used. A desiccant comprising several moisture adsorbing materials is also known as a composite desiccant.
Desiccants comprising several moisture adsorbing materials are for example described in WO2001/08784 and WO2014/051652.
WO2001/08784 describes a composition comprising a hygroscopic material dispersed in polyvinyl alcohol (PVA). In WO2001/08784 is mentioned that PVA has desiccating properties. PVA is combined with a hygroscopic material, like for example calcium chloride, phosphorous oxide, sodium silicate, potassium silicate, potassium acetate, bentonite, montmorillonite clay, silica gel, molecular sieve, monohydric compounds or polyhydric compounds. The composition according to WO2001/08784 is, according to the examples, used to impregnate a solid cardboard support to provide a cardboard support with desiccating properties.
WO2014/051652 describes a method for synergistic desiccation by using a mixture of at least one humidity attracting substance and at least one polymeric substance. The humidity attracting substance can, amongst others, be phosphorous oxide, sodium silicate, potassium silicate, potassium acetate, bentonite, montmorillonite clay, silica gel, molecular sieve, monohydric compounds, polyhydric compounds, calcium chloride, cobalt chloride and polysaccharides such as starch and cellulose. The polymeric substance can be cellulose, paper, paper products, wood fiber, paperboard, corrugated paper products and various other polymeric products.
According to the example an aqueous solution of calcium chloride is applied to the surface of a dry paperboard where after the paperboard is dried. The treated paperboard can be used as a desiccant.
The above references disclose composite desiccants for single use. After use the desiccants are disposed.
A disadvantage of many known composite desiccant materials is that it can be difficult to determine the saturation level of the desiccant, unless chemical indicators such as cobalt chloride are added. Cobalt chloride is for example a known carcinogen.
Furthermore, known desiccants were found to be difficult to mold into desirable shapes, and cannot be regenerated.